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Re: RFA: Darwin x86 alignment
On Jul 21, 2005, at 5:00 PM, Richard Henderson wrote:
On Thu, Jul 21, 2005 at 04:56:01PM -0700, Dale Johannesen wrote:
- Have flags work as now: -malign-double makes both 8,
-mno-align-double
makes both 4. Problem with that is the default is neither of these,
and
this doesn't fit neatly into gcc's model of two-valued flags; it's
also a bit
tricky to implement for the same reason.
Nah, you just remove it from target_flags, and control the two
new variables from ix86_handle_option.
OK. Think that's the better approach?
Why do you want to make these sort of arbitrary changes to your
ABI? I can't see what you win...
The compiler people are not driving this.
Of course, 4-byte alignment subjects you to a penalty for misaligned
loads and stores, and 8-byte alignment subjects you to a size penalty
for extra holes. People have been making measurements about the
issue and this is what they've come up with; I don't know details.
What I wrote isn't necessarily the final change, either.